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<a name="Hollerith-constants-support"></a>
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<a name="Hollerith-constants-support-1"></a>
<h4 class="subsection">5.1.14 Hollerith constants support</h4>
<a name="index-Hollerith-constants"></a>

<p>GNU Fortran supports Hollerith constants in assignments, <code>DATA</code>
statements, function and subroutine arguments. A Hollerith constant is
written as a string of characters preceded by an integer constant 
indicating the character count, and the letter <code>H</code> or
<code>h</code>, and stored in bytewise fashion in a numeric (<code>INTEGER</code>,
<code>REAL</code>, or <code>COMPLEX</code>), <code>LOGICAL</code> or <code>CHARACTER</code> variable.
The constant will be padded with spaces or truncated to fit the size of
the variable in which it is stored.
</p>
<p>Examples of valid uses of Hollerith constants:
</p><div class="smallexample">
<pre class="smallexample">      complex*16 x(2)
      data x /16Habcdefghijklmnop, 16Hqrstuvwxyz012345/
      x(1) = 16HABCDEFGHIJKLMNOP
      call foo (4h abc)
</pre></div>

<p>Examples of Hollerith constants:
</p><div class="smallexample">
<pre class="smallexample">      integer*4 a
      a = 0H         ! Invalid, at least one character is needed.
      a = 4HAB12     ! Valid
      a = 8H12345678 ! Valid, but the Hollerith constant will be truncated.
      a = 3Hxyz      ! Valid, but the Hollerith constant will be padded.
</pre></div>

<p>In general, Hollerith constants were used to provide a rudimentary
facility for handling character strings in early Fortran compilers,
prior to the introduction of <code>CHARACTER</code> variables in Fortran 77;
in those cases, the standard-compliant equivalent is to convert the
program to use proper character strings.  On occasion, there may be a
case where the intent is specifically to initialize a numeric variable
with a given byte sequence.  In these cases, the same result can be
obtained by using the <code>TRANSFER</code> statement, as in this example.
</p><div class="smallexample">
<pre class="smallexample">      integer(kind=4) :: a
      a = transfer (&quot;abcd&quot;, a)     ! equivalent to: a = 4Habcd
</pre></div>

<p>The use of the <samp>-fdec</samp> option extends support of Hollerith constants
to comparisons:
</p><div class="smallexample">
<pre class="smallexample">      integer*4 a
      a = 4hABCD
      if (a .ne. 4habcd) then
        write(*,*) &quot;no match&quot;
      end if
</pre></div>

<p>Supported types are numeric (<code>INTEGER</code>, <code>REAL</code>, or <code>COMPLEX</code>),
and <code>CHARACTER</code>.
</p>
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